Helpers for constructing standard HD wallet descriptors

Constructing standard HD wallet descriptors takes a fair bit of code. For example, to construct a BIP-86 single-key taproot HD wallet descriptor:

let master_xkey = ExtendedPrivKey::new_master(network, &seed)?;

let fingerprint = master_xkey.fingerprint(&secp);

let derivation_path = DerivationPath::master()
  .child(ChildNumber::Hardened { index: 86 })
  .child(ChildNumber::Hardened { index: 0 })
  .child(ChildNumber::Hardened { index: 0 });

let derived_xkey = master_xkey.derive_priv(&secp, &derivation_path)?;

let secret_key = DescriptorSecretKey::XPrv(DescriptorXKey {
  origin: Some((fingerprint, derivation_path.clone())),
  xkey: derived_xkey,
  derivation_path: DerivationPath::master().child(ChildNumber::Normal { index: 0 }),
  wildcard: Wildcard::Unhardened,
});

let public_key = secret_key.to_public(&secp)?;

let mut key_map = std::collections::HashMap::new();
key_map.insert(public_key.clone(), secret_key);

let receive_desc = Descriptor::new_tr(public_key, None)?;

It could be nice to provide helpers that would create standard HD wallet descriptors from seeds, in this case something like:

impl Descriptor {
  fn new_bip_86(secp: &Secp256k1, network: Network, seed: [u8; 32], change: bool) -> Result<(Self, DescriptorSecretKey)> {
    let master_xkey = ExtendedPrivKey::new_master(network, &seed)?;

    let fingerprint = master_xkey.fingerprint(&secp);

    let derivation_path = DerivationPath::master()
      .child(ChildNumber::Hardened { index: 86 })
      .child(ChildNumber::Hardened { index: 0 })
      .child(ChildNumber::Hardened { index: 0 });

    let derived_xkey = master_xkey.derive_priv(&secp, &derivation_path)?;

    let secret_key = DescriptorSecretKey::XPrv(DescriptorXKey {
      origin: Some((fingerprint, derivation_path.clone())),
      xkey: derived_xkey,
      derivation_path: DerivationPath::master().child(ChildNumber::Normal { index: 0 }),
      wildcard: Wildcard::Unhardened,
    });

    let public_key = secret_key.to_public(&secp)?;

    (Descriptor::new_tr(public_key, None), secret_key)
  }
}

Start with the BIP-86 example in the issue and trace the mentioned Descriptor, ExtendedPrivKey, DerivationPath, and DescriptorSecretKey APIs. Define the scope of the standard HD wallet helpers and verify that the resulting descriptor and secret key match the requested derivation and change behavior.